Gotta agree with the majority here, it'd require lots of work, art, and voice acting, even with a greatly limited support pool for each parent. Plus, it'd cause people to get upset if, say, their two favorite possible kids were attached to the same parent and both weren't possible to get in the same playthrough. Fates had a lot of characters, yes, but at least we got a third money grabber Revelations to get (almost) all of them in at the same time.